On the contact relations of high-temperature peridotites in the Serrania de Ronda,Southern Spain |
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| Authors: | AB Westerhof |
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| Institution: | Department of Petrology and Ore Geology, Geological Institute, University of msterdam, AmsterdamThe Netherlands |
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| Abstract: | Large ultramafic masses along the western margin of the Alboran Sea were emplaced in two stages. The first, “hot” stage of emplacement was post-Triassic and pre-Oligocene in age. The second, “cold” stage of emplacement was of Oligo-Miocene age.The first stage caused the development of polymetamorphic aureoles in the surrounding crustal rocks. Metamorphic conditions in the contact zone of the composite aureole series changed from HP-HT to LP-HT. The HP-HT phase of metamorphism created a primary dynamo-thermal aureole. LP-HT metamorphism took place under mainly static conditions. Present contact relations are mainly defined by the amount of secondary dislocation during hot emplacement of mantle off-shoots from the base into the higher levels of the crust. Where the primary contacts between crustal and ultramafic rocks have remained undisturbed by secondary emplacement aureoles with kinzigite series were developed. Although these rocks have partly recrystallized under LP-HT conditions, their original HP-HT characteristics are largely preserved. In other localities, however, secondary dislocation brought mantle rock in contact with lower grade zones of the primary aureole and caused the development of cordierite- and feldspar-rich hornfelses and migmatites of the cordierite-feldspar hornfels series along the new contacts of the ultramafic rocks.Metapelites with composite facies series, very similar to aureole rocks of the Serranía de Ronda but not associated with high-temperature ultramafics, are found in scattered exposures along the Spanish coast east of the Serranía de Ronda over a distance of approximately 300 km.Cold thrusting during the second stage of emplacement obscured the relations between aureole and ultramafic rocks and gave rise to tectonic contacts of younger age (imbrication). In many places broad zones of mylonite and numerous serpentine lenses formed along the younger thrust planes. |
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